If memory serves me correct the WTS light on your 6.9 runs directly off the glowplugs relay, so it not working means either the bulb is gone or the relay ain't engaging and the plugs ain't working - your hard start pretty much confirms the latter. The 6.9 glowplugs controller is known to go stupid and do things like not work at all, or get stuck on and fry the plugs. Typical treatment involves either bypassing the controller and wiring in a manual switch (preferably of the instant-on type), or retrofitting a solid-state controller system off a 7.3 truck. The first thing you should do tho is indeed check the glowplugs relay, tis on the passenger-side inner fender, and has 6 wires attached to it - three fat ones (two orange ones on the same stud, one red on the other) and three thin ones, two of the thin ones (black and purple) are obviously the control circuit whereas the fatties are the main power line for the plugs and the third thin wire (pink) is for the glowplugs light on the dash. Pull the purple wire off the relay, stick a voltmeter in it, have someone turn the truck on while you watch the numbers - 12V means controller is good and relay is bad, 0V and controller is likely gone. Also, just to make sure, jump that same wire's stud on the relay to the positive terminal of the battery - the relay should click and the glowplugs light in the cab should come on, if it happens relay is good for real.
